1. Field of the Invention
The present invention relates to stud welding devices and, more particularly, to a self-contained, portable, capacitor discharge stud welding device having a highly efficient energy transfer mechanism and capable of underwater use.
2. Description of the Prior Art
Conventional stud welders are powered by commercial power lines or by electric generating equipment. Therefore, although the welder and its associated equipment may be portable, it is not self-contained and requires an outside source of electrical power. This necessitates power supply cables which limit the mobility of the operator if used underwater. These cables may also become entangled with diving gear. The outside power supply may also present a problem if it is desired that the diver be undetected, such as in underwater demolition work involving structures controlled by a hostile power.
Conventional stud welders use electrical power, usually in the form of 100-120 volt ac, to charge a capacitor bank to approximately 150-200 volts by means of voltage doubler circuits, the charging occurring through a limiting resistor which dissipates some of the electrical energy as heat. This type of energy transfer mechanism reduces the efficiency of the energy transfer to the capacitor.
A capacitor charging circuit of this type is shown in U.S. Pat. No. 3,706,022 issued to E. E. Corey et al. on 12 Dec. 1972. That device utilizes taps on the primary winding of an output transformer. By using a time delay to switch the taps from maximum primary to secondary winding ratios to consecutively lower winding ratios, a capacitor is charged in incremental steps. The capacitor is charged through a diode bridge rectifier and a limiting resistor. While satisfactory for its intended purpose, such as in photoflash devices, the circuit requires a limiting resistor which, in turn necessitates a larger power supply to achieve the desired charge. The device is, therefore, less acceptable for situations, such as under water use, where it is desired that the power supply be kept small, self-contained and portable.